This invention relates generally to processing of carcasses and more particularly to a method and apparatus for rapid chilling of carcasses to prevent deterioration thereof.
Following the slaughter of animals for meat, it is necessary to immediately chill the carcasses of the freshly killed animals from the kill temperature to a temperature at which deterioration of the meat is substantially prevented.
One problem encountered during the chilling process is a loss of moisture from the carcasses. As well as causing undesirable condensation on the walls and ceiling of the chill room, moisture loss results in a significant reduction in the end weight of the carcass, up to about three percent, and a corresponding reduction in profit. Loss of moisture also negatively impacts the quality of the end product, particularly in the appearance of the outer portions of the carcass from which most of the moisture is lost.
The problem of moisture loss has been addressed by subjecting the carcasses to rapid chilling by super-cooled, high velocity air. This type of rapid chilling process is known in the art as xe2x80x9cquick chillxe2x80x9d or xe2x80x9cblast chillxe2x80x9d. One method of conducting a quick chill process is described in U.S. Pat. No. 4,028,774 (Allan et al.) issued Jun. 14, 1977, in which chilling is conducted by passing a carcass through a specially designed enclosure in which refrigerated air is blown over the carcass. As described in the Allen et al. patent, rapid chilling causes the formation of a thin frozen crust on the outer surface of the carcass, thus preventing deterioration of the inner portions of the carcass as it is cooled, and also reducing the moisture loss from the carcass to a relatively low level.
The rapid chilling of carcasses as described in the Allen et al. process typically reduces moisture loss to about one percent by weight, representing a substantial improvement over previously used chilling processes. However, even at this reduced level of moisture loss, there is significant degradation of meat color and quality. Therefore, it is desirable to reduce moisture loss during chilling of carcasses to the lowest possible level in order to maximize profitability and quality of the end product.
Several other methods have been developed to deal with this problem, none of which have proved to be completely satisfactory.
U.S. Pat. No. 4,325,221 (Grewar) issued Apr. 20, 1982, discloses a method of freezing the outermost layer of flesh on a carcass by contacting the carcass with a cryogenic liquid such as liquid nitrogen or liquid carbon dioxide, followed by cooling the carcass throughout by placing it in a mechanically refrigerated cold room under non-thawing conditions. As in the method described by Allan et al., the Grewar method forms a thin frozen crust on the outer surface of the carcass, and would be expected to achieve a similar level of reduction in the degree of moisture loss.
U.S. Pat. No. 4,810,515 (Bourdel) issued Mar. 7, 1989, discloses a method of cooling carcasses in which the carcasses are moved on a conveyor through a chill room. As the carcasses are cooled, they pass through a series of high humidity chambers such that the outer surface of each carcass is periodically enveloped in a water saturated atmosphere, thereby preventing excess moisture loss from the carcass. The Bourdel process however tends to be fairly expensive due to the number of high humidity chambers which must be installed inside the chill room.
U.S. Pat. No. 4,940,599 (Engler et al.) discloses a quick chill process in which carcasses are rapidly chilled by being subjected to a super-cooled atmosphere for a brief period of time. Either before or after the quick chilling of the carcasses, they are sprayed with a fine mist of water, thereby forming a thin ice layer on the outer surface of the carcasses.
It is known that where carcasses are washed with water immediately prior to the rapid chilling stage as taught by Engler et al., a thin layer of ice is formed on the outer surfaces of the carcasses. However, the layer of ice formed by this method cannot be controlled with regard to thickness, uniformity or consistency. In fact, the inventors have found that much of the water sprayed onto the carcass will either run off or be blown off by the force of the circulating air before it can form an ice layer. Thus, the formation of this type of ice layer on a carcass has a limited effect on moisture loss and improvement of meat quality. In fact, the inventors have found that a moisture loss of about 1.4 percent is typical with this type of process.
Furthermore, the inventors have found that there is little benefit to spraying carcasses with water after the quick chill process as disclosed in the Engler et al. patent, since much of the moisture loss will already have occurred before the ice layer is formed.
Therefore, there is a continued need for a chilling process which will further reduce moisture loss from carcasses.
The present invention overcomes the above-described problems of the prior art by providing a method for chilling a carcass in which the carcass is sprayed with a liquid during the chilling process. Preferably, the liquid is sprayed onto the carcass at a point in the chilling process where the outer surface of the carcass is at or near the freezing point of the liquid, resulting in the rapid formation of a uniform layer of frozen liquid on the outer surface of the carcass, which substantially prevents escape of moisture from the carcass and preserves the quality of the end product.
In preferred embodiments of the invention, the liquid sprayed onto the surface of the carcass is water, which freezes to form a layer of ice on the carcass.
By spraying the carcass at the critical point where its temperature is at or near the freezing point of the liquid, the inventors have substantially overcome the problems of the prior art discussed above, and in particular the problems of the Engler et al. patent in which an ice layer is formed on the carcass either too early or too late in the cooling process to effectively prevent moisture loss. The process of the present invention is capable of virtually eliminating moisture loss and preserving the appearance and quality of the end product.
Preferably, the carcass is sprayed inside a specially designed spray cabinet positioned within a chill room through which the carcass is transported by suspension from an overhead conveyor. The spray cabinet walls contain a plurality of water pipes, each of which is provided with a plurality of spray nozzles to direct water at the carcass. The walls of the cabinet are heated to prevent freezing of the water inside the pipes, which would otherwise occur since the chill room is maintained at a temperature well below the freezing point of water.